1. Field of the Invention
The present invention relates to an exposure device. More particularly, the present invention relates to an exposure device which scans and exposes a photosensitive layer which is sensitive to a predetermined wavelength region including a UV region (350 nm to 420 nm), with a continuously driven or pulse-driven light beam which is emitted from a high-power laser light source.
2. Description of the Related Art
A liquid crystal display (LCD) is characterized by being made more compact and thinner than a conventional CRT (cathode ray tube), and has been utilized in various fields such as portable television sets, personal computers, mobile phones, and the like, and a market therefore has been increasing. A liquid color filter is a member for achieving the color LCD, and is structured such that three original color patterns of red, green and blue are regularly arranged on a glass substrate. In accordance with broadened applications of the LCD, there is a demand for the liquid color filters of larger size and higher accuracy.
Conventionally, an exposure device that is used during the manufacturing process of the liquid crystal display uses one of three roughly-defined methods such as a proximity method, a mirror projection method, and a stepper method. Among these, the exposure device using the proximity method is usually used for the manufacture of the liquid color filter (especially for a photolithography process). When the exposure device using the proximity method carries out photolithography, a UV light is irradiated onto one surface of a substrate through a mask to expose a photoresist (photosensitive material).
However, in the exposure device using the proximity method, since a mask and a substrate are disposed in close proximity to each other, such as a few dozen μm to expose at one time, problems described below may occur:    (1) a large and expensive mask must be used, the mask is easily damaged by contact with the substrate, and a cost of the mask increases;    (2) since the distance between the mask and the substrate during the exposure is small, a holding mechanism and an aligning mechanism with high accuracy are needed to hold and align the mask and the photosensitive material;    (3) a temperature stabilizing mechanism becomes necessary to prevent deterioration of rendering accuracy due to a thermal contraction of the mask and the substrate;    (4) since a super high pressure mercury lamp whose life duration is short is used as a UV light source, the super high pressure mercury lamp must be replaced frequently; and    (5) more electric power is consumed.
The exposure device during the manufacturing process of a printed circuit board (PCB) usually uses a concurrent exposure method in which a photosensitive material is exposed at one time by a mercury lamp using a film mask. Regarding the exposure of the PCB, the higher the packaging density at which components for the exposure device are packaged, the higher the accuracy and miniaturization with which the circuitry are patterned. However, since the mercury lamp uses the film mask, a problem is caused by film contraction due to a change of temperature and/or humidity and a change of temperature at the substrate side, thus making it difficult to obtain more accurate circuit patterning than in the exposure device of the current technology. If a glass mask is used instead of the film mask, a problem with the film contraction can be eliminated. However, the glass mask is expensive, and handling thereof is difficult.
During the manufacturing process of the PCB, mass production of various products using a small scale production scale or production of requested items (so-called on-demand production) has often been employed in recent years. However, the concurrent exposure method needs a lot of time to prepare the mask alignment exposure, thus resulting in being inappropriate for the on-demand production. Further, with the concurrent exposure method, dust or defects on the mask decrease yields. Moreover, the super high-pressure mercury lamp and the mask are needed for the mask alignment exposure so that the running costs increases. Since a strong demand for signals with higher frequency tends to result in a higher demand for reproducibility of the PCB patterning, performance tests must be conducted on trial substrates on the actual mass-production line in order to guarantee the performance. Thus, even the mass-production line has a high demand for an exposure device that does not rely on mask alignment exposure but can implement a flexible production.
Conventionally, the manufacturing process of a plasma display panel (PDP) has mainly used the exposure device by the proximity method described above. However, since the display size of the PDP is large, a problem is caused in that a mask size becomes larger, whereby the mask manufacture becomes more expensive. Further, since the plasma display has a high demand for the on-demand production, use of an appropriate exposure device for the on-demand production is needed. Moreover, in the same manner as the exposure for the liquid crystal display (LCD) or the printed circuit board (PCB), a problem is caused with the operating costs due to the mask alignment exposure.
Lately, as an exposure device for a printed circuit board or a plasma display panel, a laser scanning and exposing device has been put into practical use. The above-described problems of the mask alignment exposure can be solved by the laser scanning and exposing device. However, at present, the laser scanning and exposing device is hardly popular. This is because a conventional laser scanning and exposing device uses an argon laser of several watts as a light source. Therefore, the following problems occur:    (1) in order to obtain an exposure speed (productivity) equal to that of the mask aligning exposure device, use of a material to be exposed with high sensitivity becomes necessary;    (2) a gas laser itself is expensive, whereby the manufacturing and maintenance costs of the entire device become high;    (3) for a conventional material to be exposed, since the light source power is low, productivity is extremely low;    (4) an exposure device of a certain type has a light source whose wavelengths are 488 nm and 532 nm, within a visible wavelength region, whereby dark room work becomes necessary; and    (5) a special material to be exposed with high sensitivity and having sensitivity in a visible wavelength region is expensive, and has insufficient stability.